Fishing boats, for example, would be guarded safe in fishing sailings if information, for example, a weather map is available while off shore, and therefore they make it a practice to equip the facilities to communicate such information as a weather map by radio facsimile communications. Accordingly, the radio communications systems on board are designed to work as radio phone and also as radio facsimile by a switchover operation or like, wherein the radio phone system handles audio sound waves and the radio facsimile system handles the signals produced by scanning over images drawn on papers or like, but in no case the facsimile system has any separate utility of handling the signals differently derived from voice or sound waves.
In the case where the SSB system is applied to the facsimile communication for the merit that the SSB system can cover a longer distance, difficulties have been found. That is, when some disagreement or error arises at the receiver's frequency as compared with the transmitter's frequency, such an error causes the phenomena distinctive to the SSB system, that is, the receiver's demodulated signals for the facsimile will have a frequency with an error correspondent to the error arisen in the transmission.
In the meantime, the data transmission by the facsimile is required to meet the strict standard which provides that the allowable error range in frequency should be within several Hz in the communications. Therefore, in the case of carrying out the facsimile communication by the radio SSB transmission system, an error between the transmitter's frequency and the receiver's frequency for facsimile signals should be controlled within several Hz.
However, the SSB system which has been generally employed for the merit of lower cost facilities is difficult to meet the strict provision as noted, and as a result, a communication facilities requiring higher cost can not be dispensed from the facsimile system. In other words, for the reason of cost problem, the facsimile system has been impeded from a level of popular use or further popularization.
This invention has proceeded from the background as noted above and has an object of offering a facsimile communication apparatus which enables superior facsimile communication with use of the radio SSB system, with overcoming the conventional problem of an frequency error between a transmitter and a receiver.